Coatings are typically applied to the interior of metal food and beverage containers to prevent the contents from contacting the metal surface of the container. Contact with certain foods, particularly acidic products, can cause the metal container to corrode. This corrosion results in contamination and deterioration in the appearance and taste of the food or beverage product.
The internal protective coating applied to metal cans is typically one that has low extractibles to avoid contamination of the contents. The coating may also be substantially defect-free, and possess high resistance to a wide variety of foods and beverages. Good adhesion to metal surfaces is also desired, as is good wetting, to ensure complete coverage of the metal and to protect the metal during baking and forming operations. The high temperatures needed to achieve rapid curing speeds, however, often result in blistering of the coating. Blistering typically occurs as cure temperature passes through the boiling point of water and can result in incomplete or weakened coverage of the can interior. After can fabrication, the coating should withstand the relatively stringent temperature and pressure requirements to which cans are subjected during food processing and should provide the necessary level of corrosion resistance to the cans once filled.